Here is the full list of all 50 Eldest Souls achievements.
Defeat Eos, God of Unity while taking 0 damage.
Gain the Abyssal Eye
Defeat Azikel, God of Light while taking 0 damage.
Defeat the Guardian while taking 0 damage.
Defeat Eksyll in Abyss Mode.
Defeat Aryana in Abyss Mode.
Defeat The Warden of Purity in Abyss Mode.
Defeat The Deer God in Abyss Mode.
Defeat Drakmur in Abyss Mode.
Gain the Kindled Heart of Fire
Defeat Hyem in Abyss Mode.
Hit enemies with a Shard attack 200 times
Defeat Azikel in Abyss Mode.
Defeat Eos in Abyss Mode.
Have at least 10 Windleaves active at once.
Defeat the Guardian in Abyss Mode.
Perform 3 Perfect Counters in a row against any Boss.
Finish the game without activating any Shard or Infusions.
Gain the Blessed Trueice Prism
Obtain the Empty Vessel
Defeat the Watchdog while taking 0 damage.
Die to a rolling log.
Defeat Eksyll
Reach the Steps of Ascension
Defeat Drakmur, the Nightmare
Defeat Aryana, First of the Moon.
Defeat The Deer God and the Warden of Purity.
Gain the Blessed Feather of Dawn
Defeat Hyem of the Frigid Waste.
Deliver the bag of crowns to Edelon.
Reach Concord Sanctuary
Defeat Eos, God of Unity
Defeat Azikel, God of Light.
Retry a Boss 10 times in a row.
Hit enemies with a thrust attack 200 times
Reach the Crossroads
Defeat the Guardian.
Hit an enemy with Windslide, Berserker Slash, or Counter 20 times.
Die to a Boss.
Talk with Rass
Deliver the harp string to Edd
Defeat the Watchdog.
Reach Crusader's Landing
Defeat Hyem while taking 0 damage.
Defeat The Deer God and the Warden of Purity while taking 0 damage.
Defeat Aryana, First of the Moon while taking 0 damage.
Defeat Drakmur, the Nightmare while taking 0 damage
Maintain 4 stacks of Berserker for 30s.
Reach the ending without dying once.
Gain the Blessed Hunter's Charm